Method for debindering of powder molded body

ABSTRACT

A method for debindering of powder molded body, including dipping, in an extracting solution an aqueous surfactant solution, a ceramic powder or metal powder molded body containing a binder with at least two kinds of binder components, to selectively extract and remove at least one kind of binder component from the molded body, and then removing the binder components remaining in the molded body after extraction. This debindering method permits rapid debindering while preventing the generation of defects such as cracks and the like, is highly safe to human health and environment, and requires a low facility cost.

This application is a 371 of PCT/JP01/05782 filed Jul. 4, 2001.

TECHNICAL FIELD

The present invention relates to a debindering method used for removinga binder from a powder molded body containing a binder consisting of atleast two kinds of binder components.

BACKGROUND ART

When a ceramic powder or metal powder molded body is produced byextrusion, injection or the like, a binder is added into a ceramicpowder or a metal powder in order to obtain higher moldability. Thebinder component used is determined in view of the shape, raw material,molding method, etc. of the molded body to be produced, and it is notrare to use a binder consisting of at least two components.

In producing, for example, a molded body of honeycomb form used inproduction of, for example, a carrier for exhaust gas purificationcatalyst or a filter for diesel particulate, there has come to be used athermoplastic binder which is a mixture of a water-insoluble wax and athermoplastic resin, in place of a conventional binder which is awater-soluble thermosetting methyl cellulose, because the partitionwalls of honeycomb structure have become thinner (25 to 100 μm) andconsequently higher fluidity during extrusion and higher shaperetainability after extrusion have become necessary.

Such a thermoplastic binder contains no water therein and thereforerequires no drying step unlike the case using a water-soluble binder;however, the weight ratio of binder component in molded body isinevitably large. Therefore, a large amount of a binder must be removedfrom the molded body during the debindering step, and it is an importanttask to conduct a debindering treatment rapidly without generating anydefect in the molded body.

For debindering of molded body, it is generally conducted to heat amolded body to allow the binder in the molded body to vaporize anddecompose thermally. This debindering method has been used also indebindering of the above-mentioned molded body of honeycomb form.Meanwhile, a thermoplastic binder has been used in producing a moldedbody by injection and, for debindering of the produced molded body, amethod is known in which part of the binder used is removed bydissolution (extraction) using an organic solvent and then the remainingbinder is removed by heating (see JP-B-59-27743).

In the method for debindering of molded body by heating a molded body toallow the binder contained therein, to vaporize and decompose thermally,however, the thermal decomposition of organic binder generates a largeamount of a decomposition gas (e.g. CO₂) and accordingly gives a largeburden to the environment. Further, the abrupt heat generation duringthe thermal decomposition of binder gives rise to a temperaturedifference inside the molded body; and the thermal stress caused by thistemperature difference, plus the pressure of decomposition gas or thedimensional change caused by decomposition tend to generate defects suchas cracks and the like particularly in a molded body of relatively lowstrength, such as honeycomb molded body of thin partition walls. Inorder to prevent such defects, it is necessary to slow the temperatureelevation during the heating of molded body and make small the heatgeneration inside the molded body, which makes long the debinderingtime.

In the method for debindering of molded body by extracting the bindercontained in a molded body, with an organic solvent, there is used anorganic solvent which gives adverse effects on human health and theenvironment and which may cause fire; this invites the deterioration ofworking environmental, reduced safety and an increase in the incidentalfacility required for emission gas treatment, etc.

The present invention has been made in view of the above-mentionedsituation and aims at providing a method for debindering of powdermolded body, which enables a short time and rapid debindering treatmentwhile preventing the generation of defects such as cracks and the like,which has high safety to human health and environment, and whichrequires a low facility cost.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided a method fordebindering of powder molded body, characterized by dipping, in anextracting solution composed of an aqueous surfactant solution, aceramic powder or metal powder molded body containing a bindercomprising at least two kinds of binder components, to selectivelyextract and remove at least one kind of binder component from the moldedbody, and then removing the binder components remaining in the moldedbody after extraction.

In the present invention, it is desirable from the standpoint ofpreventing the cracks generating during the extraction from the moldedbody that at least 40% by volume of the binder component to beselectively extracted is extracted and removed before the linearexpansion of the molded body during the extraction step reaches 50%relative to the linear expansion of the molded body when no extractionand removal is made. Even if the linear expansion of the molded bodyduring the extraction step is 50% or more relative to the linearexpansion of the molded body when no extraction and removal is made, itis desirable to allow the molded body to make uniform expansion from thestandpoint of preventing the cracks generating during the extractionfrom the molded body. It is preferred to selectively extract and removeat least one kind of binder component from the molded body, wash theresulting molded body with water, remove the water remaining in oradhering to the molded body, and then heat the molded body to remove thebinder components remaining in the molded body without being extractedby the extracting solution, because this operation makes easy theremoval of water from the molded body and prevents the generation ofcracks in the molded body during its drying.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a), 1(b) and 1(c) show generation of cracks in the fired bodysobtained in Examples. FIGS. 1(a), 1(b) and 1(c) show the cracksgenerated in the ends of the fired bodys obtained in Example 1, Example4 and Comparative Example, respectively.

FIG. 2 shows the temperature of an aqueous solution and the degree ofdebindering and expansion coefficient of a molded body when the moldedbody was dipped in the aqueous solution and the solution was subjectedto rapid temperature elevation.

FIG. 3 shows the temperature of an aqueous solution and the degree ofdebindering and expansion coefficient of a molded body when the moldedbody was dipped in the aqueous solution and the solution was subjectedto slow temperature elevation.

BEST MODE FOR CARRYING OUT THE INVENTION

In the method for debindering of powder molded body according to thepresent invention, a ceramic powder or metal powder molded bodycontaining a binder consisting of at least two kinds of bindercomponents is debindered. First, the molded body is dipped in anextracting solution consisting of an aqueous surfactant solution toselectively extract and remove at least one kind of binder componentfrom the molded body while leaving at least one other kind of bindercomponent in the molded body.

By thus selectively extracting and removing at least one kind of bindercomponent from the molded body while leaving at least one other kind ofbinder component in the molded body, the molded body can keep therequired shape even after the extraction owing to the action of thebinder component remaining in the molded body and can be free fromdeformation.

The binder component remaining in the molded body without beingextracted by the extracting solution is removed finally by various meanssuch as thermal decomposition, combustion, vaporization, sublimation,chemical decomposition, supercritical fluid extraction and the like. Inthe present invention, since only the binder component remaining in themolded body without being extracted is removed finally, the amount ofthe binder removed finally can be made small. As a result, the heatgenerated or absorbed or amount of decomposition gas generated duringthe binder removal is small and the dimensional change of the moldedbody taking place associated with the binder removal is also small;consequently, the damage (e.g. cracks generation) of the molded body issuppressed, the treatment time is short, and the load to environment issmall.

Further in the present invention, since the extracting solution forbinder is an aqueous surfactant solution, the safety to human health andenvironment is high and the breakout of fire can be prevented. As aresult, the incidental facility required for emission gas treatment,etc. can be made small, resulting in a reduced equipment cost.

However, the selective extraction of the binder from the molded body isconducted at a temperature not lower than the melting point of thebinder component to be extracted; hence, during the temperatureelevation for conducting the extraction, the binder gives rise to volumeexpansion and shrinkage and generates a stress, which may generatecracks in the molded body.

It is preferred in the present invention to conduct selective extractionof binder under such a condition that at least 40% by volume of thebinder component to be extracted and removed is removed before thelinear expansion of the molded body reaches 50% relative to the linearexpansion of the molded body when no extraction and removal is made.Such selective extraction can be conducted, for example, by conductingpreliminary extraction at a temperature lower than the melting point ofthe binder component to be extracted, until the binder component isextracted to a predetermined level or more, and thereafter heating theextracting solution (containing the molded body) to a temperature equalto or higher than the melting point of the binder component, to conductnormal extraction. The preliminary extraction can be conducted, forexample, by (1) increasing the temperature of the extracting solution(containing the molded body) at a low temperature elevation rate of 20°C./hr or less, or (2) keeping the above extracting solution for a givenlength of time at a temperature lower than the melting point of thebinder component.

By thus using a low temperature elevation rate or keeping the extractingsolution at a temperature lower than the melting point of the bindercomponent, the binder component is extracted, the binder amount in themolded body is reduced, and the molded body shows volume expansion owingto its temperature increase. Therefore, the volume expansion of themolded body is small and the stress generated is small as compared withthe case when the temperature elevation rate of the extracting solutionis not lower than the above-mentioned predetermined level; the binder ispartially extracted and removed and the molded body becomes porous;consequently, the stress generated is relaxed, generation of cracks isprevented, and the selective extractability for the binder component isimproved.

A study by the present inventor revealed that in the selectiveextraction of binder from molded body, the molded body undergoes twocontradictory actions, i.e. expansion and shrinkage because there takeplace the expansion of binder and the shrinkage caused by the progressof extraction simultaneously. A further study by the present inventorfound out that by conducting slow extraction at a temperature elevationrate (of the extracting solution) of not higher than a predeterminedlevel or by keeping the extracting solution for a predetermined lengthof time at a temperature lower than the melting temperature of thebinder, it is possible to prevent the generation of cracks in the moldedbody and increase the selective extractability for the binder component.Further in the selective extraction of the binder component, thetemperature decrease is preferably conducted slowly because in thetemperature decrease, a stress is generated owing to the shrinkage ofthe residual binder.

In the above (1), the temperature elevation rate of the extractingsolution is preferably 10° C./hr or less, particularly preferably 5°C./hr or less. In the above (2), it is desired that the extractingsolution is kept for 2 to 6 hours at a temperature lower by 5 to 10° C.than the melting point of the binder component. The temperature decreaserate during the cooling is preferably 80° C./hr or less, more preferably60° C./hr or less, further preferably 30° C./hr or less.

In the present invention, even when the linear expansion of the moldedbody caused by the volume expansion of the binder during the extractionis 50% or more relative to the linear expansion of the molded body whenno extraction is made, the molded body can be allowed to generate nocrack by allowing the expansion to take place uniformly. For example,when the molded body of honeycomb form is dipped directly in theextracting solution of 70° C., the molded body shows a linear expansionof about 2%; in this case, however, since the partition wall thicknessof the honeycomb molded body is small and the gap portion of thehoneycomb cells is momentarily filled with the extracting solution of70° C., the honeycomb molded body gives rise to uniform expansionmomentarily, resulting in no crack formation. Such an operation ispreferred because the extraction time can be shortened significantly.

As mentioned above, an aqueous surfactant solution is used as theextracting solution for binder. As a result, in drying of the moldedbody conducted after the selective extraction of the binder componentfrom the molded body, the aqueous surfactant solution generates bubblesand these bubbles make difficult or slow the removal of the waterremaining in the molded body or adhering to the molded body; further,since the outer surface of the molded body dries quickly, a tensilestress appears and cracks tend to generate. Hence, in the presentinvention, it is preferred to wash the molded body after selectiveextraction of binder, with water and then absorb/remove the waterremaining in the molded body, with a water-absorbent substance such aspaper towel, porous ceramic or the like. Further, in the drying of themolded body obtained, it is preferred to conduct non-circulating dryingbecause when drying is conducted by allowing a gas flow (generated by acirculating fan or the like) to collide with the molded body, the moldedbody is dried non-uniformly. After the drying of the molded body, thebinder components remaining therein are removed, whereby the debinderingof molded body is completed.

In the present invention, the binder consists of the component to beextracted and removed from the molded body by the extracting solutionand the component to be decomposed and removed by the heat applied. Awax is preferred as the former component and an EVA is preferred as thelatter component. When the binder component to be extracted and removedby the extracting solution is a wax, the wax becomes a liquid in theextracting solution when extraction is conducted at a temperature notlower than the melting point of the wax, and easy extraction ispossible.

After the extraction, the extracting solution is cooled to around roomtemperature. Thereby, the extracted wax component solidifies and floatsat the top of the extracting solution, and the solidified wax isseparated and recovered. Thus, both the extracting solution and the waxcan be reutilized. Incidentally, in the extraction, it is preferred toshake the molded body dipped in the extracting solution or move theextracting solution in order to always contact the molded body with afresh portion of the extracting solution, because such contact canachieve a higher degree of extraction.

The surfactant used in the present invention is preferably any one kindof surfactant selected from the group consisting of nonionicsurfactants, anionic surfactants, cationic surfactants and amphotericsurfactants, or a combined surfactant consisting of at least two kindsselected from the above group. In general, surfactants act to aninterface between two different substances and reduce the tension of theinterface, and have functions of penetrability increase, wettabilityincrease, fluidity increase, emulsification, dispersion and dissolution.In the present invention, the surfactant is presumed to effectivelyexhibit mainly penetrability increase, wettability increase,emulsification and dispersion.

It is believed that anionic surfactants and nonionic surfactants havethe above functions in combination and that cationic surfactants andamphoteric surfactants promote the above functions depending upon theway they are used. Therefore, by appropriately combining at least twokinds of the above surfactants, the resulting extracting solution canhave two functions, i.e. a function of penetrating into the interfacebetween the binder and the powder both constituting the molded body andtaking out the binder and a function of dispersing the taken-out binderin water, whereby extraction can be conducted more easily.

More specific examples of the surfactants are mentioned. As theamphoteric surfactants, there can be mentioned amine oxide type andalkyl betaine type; as the nonionic surfactants, there can be mentionedalkanolamide type; and as the anionic surfactants, there can bementioned salts of alkyl ether sulfates and salts of alkyl sulfates. Useof any kind of surfactant selected from these surfactants is preferredbecause a high degree of debindering can be obtained.

In the present invention, there is no particular restriction as to thekind of the ceramic powder or metal powder constituting the molded bodyto be debindering. There is no particular restriction, either, as to thedimension or form of the molded body; however, the present debinderingmethod is particularly effective to a molded body of small wallthickness into which the extracting solution can easily penetrate, forexample, a molded body of honeycomb form.

The present invention is described in more detail below by way ofExamples. However, the present invention is in no way restricted bythese Examples.

EXAMPLE 1

To 100% by weight of a ceramic powder were added, as a binder, a wax(54% by weight of a paraffin wax and 8% by weight of a microcrystallinewax) and 35% by weight of an EVA and, as a lubricant, 3% by weight ofoleic acid. The resulting mixture was kneaded at 100° C. for 2 hoursusing a pressure kneader. The kneaded material was molded into acylinder of 115 (diameter)×200 (length) using a vacuum pug mill. Thecylinder was molded into a honeycomb form of 112 (diameter)×180 (length)using a plunger type extruder. The honeycomb form had a wall thicknessof 2 mil (51 μm) and a cell density of 600 cells/in.² (93 cells/cm²).

The thus obtained molded body was dipped into an aqueous solutioncontaining 4% of a dihydroxylethylalkylamine oxide. The aqueous solutionwas heated at a temperature elevation rate of 20° C./hr, kept at 60° C.for 2 hours, then cooled at a cooling rate of 60° C./hr, washed withwater, and dried in a dry air of 50° C. to obtain aextraction-debindered body. An analysis of the extracting solution afterthis operation indicated that only the wax was extracted selectively and35% of the wax was removed by the extraction. The extraction-debinderedbody was heated to 400° C. at a temperature elevation rate of 10° C./hrin an atmosphere in which the oxygen concentration was reduced to 10%,to remove the remaining binder components by the heating. The resultingmaterial was fired at 1,430° C. for 4 hours, which generated very smallcracks [see FIG. 1(a)].

EXAMPLE 2

A molded body obtained in the same manner as in Example 1 was dipped inan aqueous solution containing 10% of lauryldimethylamine oxide, anddebindering by extraction was conducted under the same conditions as inExample 1. As a result, 50% of the wax was removed by the extraction.The extraction-debindered body was heated to 400° C. at a temperatureelevation rate of 10° C./hr in the atmosphere to remove the remainingbinder components by the heating. The resulting material was fired at1,430° C. for 4 hours, which generated very small cracks.

EXAMPLE 3

An extraction-debindered body obtained in the same manner as in Example2 was debindered by heating, under the same conditions as in Example 1and then fired, whereby was obtained a fired body having no crack.

EXAMPLE 4

A molded body obtained in the same manner as in Example 1 was dipped inan aqueous solution containing 2.5% of a dihydroxylethylalkylamine oxideand 5% of coconut oil fatty acid diethanolamide, and debindering byextraction was conducted under the same conditions as in Example 1. As aresult, 54% of the wax was removed. The extraction-debindered bodyobtained was fired under the same conditions as in Example 2, whichgenerated very small cracks [see FIG. 1(b)].

EXAMPLE 5

An extraction-debindered body obtained in the same manner as in Example4 was debindered by heating, under the same conditions as in Example 1and then fired, whereby was obtained a fired body having no crack.

EXAMPLE 6

A molded body obtained in the same manner as in Example 1 was dipped inan aqueous solution containing 7.5% of dimethyllaurylamine oxide and2.5% of an alkylalkanolamide, and debindering by extraction wasconducted under the same conditions as in Example 1. As a result, 65% ofthe wax was removed. The extraction-debindered body obtained was firedunder the same conditions as in Example 2, which generated very smallcracks.

EXAMPLE 7

An extraction-debindered body obtained in the same manner as in Example6 was debindered by heating, under the same conditions as in Example 1and then fired, whereby was obtained a fired body having no crack.

EXAMPLE 8

A molded body obtained in the same manner as in Example 1 was dipped inan aqueous solution containing 6% of ammonium salt of lauryl sulfate,2.5% of dimethyllaurylamine oxide and 1.5% of an alkylalkanolamide, anddebindering by extraction was conducted under the same conditions as inExample 1. As a result, 80% of the wax was removed. Theextraction-debindered body obtained was debindered by heating and firedunder the same conditions as in Example 2, whereby was obtained a firedbody having no crack.

EXAMPLE 9

A molded body obtained in the same manner as in Example 1 was dipped inan aqueous solution containing 2.5% of dimethyllaurylamine oxide and7.5% of ammonium salt of lauryl sulfate. The temperature of the aqueoussolution was increased at a temperature elevation rate of 20° C./hr; theaqueous solution was kept at 70° C. for 2 hours and then cooled at acooling rate of 60° C./hr; the resulting molded body was washed withwater and dried to obtain an extraction-debindered body. Almost 100% ofthe wax was removed by the extraction. The extraction-debindered bodywas debindered by heating and fired, under the same conditions as inExample 2, whereby was obtained a molded body having no crack.

EXAMPLE 10

An extraction-debindered body obtained in the same manner as in Example9 was heated to 400° C. in the atmosphere at a temperature elevationrate of 30° C./hr to remove the remaining binder components by theheating. The resulting molded body was fired at 1,430° C. for 4 hours toobtain a fired body having no crack.

COMPARATIVE EXAMPLE

A molded body obtained in the same manner as in Example 1 was heated ata temperature elevation rate of 10° C./hr in an atmosphere in which theoxygen concentration was reduced to 10%, to conduct debindering byheating (no extraction was conducted). The resulting material was firedat 1,430° C. for 4 hours, which generated large cracks [see FIG. 1(c)].

EXAMPLE 11

A molded honeycomb material of 112 (diameter)×180 (length) was obtainedin the same manner as in Example 1. The molded honeycomb material had awall thickness of 2 mil (51 μm) and a cell density of 600 cells/in.² (93cells/cm²). The molded body was dipped in an aqueous solution containing2.5% of dimethyllaurylamine oxide and 7.5% of ammonium salt of laurylsulfate. The temperature of the aqueous solution was increased at atemperature elevation rate of 5° C./hr; the aqueous solution was kept at70° C. for 2 hours and cooled at a cooling rate of 60° C./hr; and themolded body was washed with water. The resulting molded body was placedon a paper towel to absorb and remove the water remaining in the moldedbody, and then dried in a dryer having no circulation fan. The dryingwas conducted in a windless state in the above dryer by increasing thetemperature of the molded body at a temperature elevation rate of 10°C./hr and then keeping the molded body at 50° C. for 16 hours, wherebywas obtained an extraction-debindered body. An analysis of theextracting solution after extraction indicated that only the wax wasextracted selectively, and the total amount (100%) of the wax wasremoved by the extraction. The extraction-debindered body was heated to400° C. at a temperature elevation rate of 10° C./hr in the atmosphereto remove the remaining binder components by the heating, and then firedat 1,430° C. for 4 hours. As a result, a fired body having no crack wasobtained.

TABLE 1-1 Example 4 Dihydroxylethyl- Example alkylamine Dimethyllauryl-Example 1 Example 2 oxide/coconut amine Dihydroxylethyl- Lauryldimethyl-Example 3 oil fatty acid Example oxide/alkyl- Surfactant alkylamineoxide amine oxide Same as left diethanolamide Same as left alkanolamideExtraction temp. (° C.) 60 60 60 60 60 60 Temp. elevation rate 20 20 2020 20 20 During extraction (° C./hr) Cooling rate during 60 60 20 60 6060 Extraction (° C./hr) Degree of extraction (%) *1 35 50 50 54 54 65Extraction yield (%) 20 40 60 40 40 60 Temp. elevation rate 10 10 10 1010 10 During heat debindering (° C./hr) Debindering atmosphere O₂ 10%Air O₂ 10% air O₂ 10% air Cracks in fired body *2 Δ Δ ◯ Δ ◯ Δ TABLE 1-2Example 8 Dimethyllauryl- Example 9 Example 11 amine Dimethyllauryl-Dimethyllauryl- oxide/ammonium amine amine Example 7 salt of lauryloxide/ammonium oxide/ammonium Same as in sulfate/alkyl- salt of laurylExample 10 salt of lauryl Comp. Example Surfactant Example 6alkanolamide sulfate Same as left sulfate — Extraction temp. (° C.) 6060 70 70 70 — Temp. elevation rate 20 20 20 20  5 — During extraction (°C./hr) Cooling rate during 60 60 60 70 60 — Extraction (° C./hr) Degreeof extraction (%) *1 65 80 100  100  100   0 Extraction yield (%) 60 8080 80 100  — Temp. elevation rate 10 10 10 30 10 10 During heatdebindering (° C./hr) Debindering atmosphere O₂ 10% Air air air air O₂10% Cracks in fired body *2 ◯ ◯ ◯ ◯ ◯ x *1: weight relative to wax *2:◯: No crack, Δ: Very small cracks, x: Large cracks Firing was conductedon samples showing no crack during extraction.

Table 1 shows the results of Examples 1 to 11 and Comparative Example.As seen from the results, cracks are less likely to appear in Examples 1to 11 where binder removal was conducted using extraction debinderingand heat debindering in combination, than in Comparative Example wherebinder removal was conducted using heat debindering alone. Further, useof appropriately combined surfactants can increase the degree ofextraction, and a higher degree of extraction gives less and smallercracks.

As seen from the results of Examples 2-3 and Examples 9-10, when thedegree of extraction for binder is low and extraction is insufficient, acooling rate larger than a certain level gives increased cracks; and asseen from the results of Examples 9-10 and Example 11, a temperatureelevation rate (during extraction) smaller than a certain level preventsgeneration of cracks. Incidentally, even at a low degree of extraction,control of oxygen concentration can prevent rapid combustion of binderand generation of cracks.

EXAMPLE 12

A molded honeycomb material of 112 (diameter)×180 (length) having thesame wall thickness and cell density as in Example 1, obtained in thesame manner as in Example 1 was dipped in an aqueous solution containing2.5% of dimethyllaurylamine oxide and 7.5% of ammonium salt of laurylsulfate. The temperature of the aqueous solution was increased at asmall temperature elevation rate of 5° C./hr or at a large temperatureelevation rate of 60° C./hr, after which the solution was kept at 70° C.for 2 hours and then cooled at a cooling rate of 60° C./hr. In FIGS. 2and 3 are shown the temperature of aqueous solution and the degree ofdebindering and expansion coefficient of molded body, all recorded inthe above operation.

As appreciated from FIGS. 2 and 3, when a small temperature elevationrate of 5° C./hr is employed, as compared with when a large temperatureelevation rate of 60° C./hr is employed, extraction proceeds while theexpansion of molded body is being kept low.

INDUSTRIAL APPLICABILITY

As explained above, the debindering method of the present inventionenables a short time and rapid debindering treatment while suppressingthe generation of defects such as cracks and the like. Further, thepresent debindering method has high safety to human health andenvironment and requires a low facility cost.

What is claimed is:
 1. A method for debindering a powder molded body,the method comprising: dipping, in an extracting solution comprising anaqueous surfactant solution, a ceramic powder or metal powder moldedbody containing a binder comprising at least two kinds of bindercomponents, selectively to extract and remove at least 40% by volume ofat least one kind of binder component from the molded body before linearexpansion of the molded body reaches 50% relative to linear expansion ofthe molded body when no extraction and removal takes place, and thenremoving the binder components remaining in the molded body afterextraction.
 2. A method for debindering a powder molded body accordingto claims 1, wherein the molded body is allowed to expand uniformlyduring the extraction step.
 3. A method for debindering a powder moldedbody according to claim 1, comprising: selectively extracting andremoving at least one kind of binder component while leaving at leastone other kind of binder component in the molded body, washing theresulting molded body with water, removing the water remaining in oradhering to the molded body, and then heating the molded body todecompose and remove the binder components remaining in the molded bodywithout being extracted by the extracting solution.
 4. A method fordebindering a powder molded body according to claim 1, wherein thebinder component extracted and removed by the extracting solution is awax and the binder component decomposed and removed by the heating is aresin.
 5. A method for debindering a powder molded body according toclaim 1, wherein the surfactant is a surfactant selected from the groupconsisting of nonionic surfactants, anionic surfactants, cationicsurfactants, and amphoteric surfactants, or mixtures thereof.
 6. Amethod for debindering a powder molded body according to claim 5,wherein the surfactant is a surfactant selected from the groupconsisting of amine oxide surfactant, alkyl betaine surfactant,alkanolamide surfactant, alkyl ether sulfate salt surfactant, and alkylsulfate salt surfactant.
 7. A method for debindering a powder moldedbody according to claim 1, wherein the binder component extracted andremoved by the extracting solution is a wax and the extraction isconducted at a temperature not lower than the melting point of the wax.8. A method for debindering a powder molded body according to claim 1,wherein the extraction is conducted by shaking the molded body dipped inthe extracting solution, or moving the extracting solution.
 9. A methodfor debindering a powder molded body according to claim 1, wherein themolded body has a honeycomb form.
 10. A method for debindering a powdermolded body according to claim , wherein a temperature of the extractingsolution containing the molded body is increased at an elevation ratethat does not exceed 20° C./hr.
 11. A method for debindering a powdermolded body according to claim 1, wherein a temperature of theextracting solution is maintained at a temperature lower than themelting point of the binder component.